The present invention relates to moving or positioning an element or device such as an optic or lens.
Stages for positioning optics are common, including stages that move an optic along the optical axis. They are frequently used to move an optical element to affect the focus or collimation of an optical beam in an optical system. Such systems are used for applications ranging from microscopes to systems requiring a focused laser beam for drilling. As the precision, accuracy and speed requirements of such systems increases, the old stage designs become inadequate.
The typical optic positioning stage uses one or more linear bearings mounted parallel to but offset from the optical axis. The optic is driven using a screw, which is also mounted, parallel to but offset from the optical axis. This arrangement produces torques about the optical axis resulting in both lateral and angular perturbations to the optical element resulting in translation and or distortion of the optical beam. Screw based stages are also not particularly fast. Bearing stages in general contain stiction and friction that can cause degradation of overall servo performance.
Alternatives to slow screw drives are available. One such alternative is a linear motor. They can be commutated multiple pole motors or single phase voice coils. The magnet can move or the coil can move. Linear motors have been used to move optics but they are still mounted off axis, which causes torques. Flexures are a good way to guide a linear motor over a short stroke. Flexures can be arranged to guide the linear motor symmetrically about the force axis. This arrangement is common with reciprocating compressors and pumps.
The ideal arrangement would use a voice coil motor to produce quick motion. The coil would be guided symmetrically about the force axis using flexures. To make the stage useful for optical systems and not produce torques the optical beam must be allowed to pass through the center of the motor, which is along the force and constraint axis. There must be a clear aperture through the center of the stage.
Capobianco et al 4,671,638 (June 1987) teaches about a “moving coil electromagnetic actuator and shutter employing same”. Capobianco is differentiated from the present invention by both purpose and means. Capobianco uses a moving coil motor and planar flexures to affect an optical beam. However, the flexures are used for rotational rather than translation motion. The optical axis, the flexure axis and the coil axis are parallel and offset from each other. It is actually a planar device to create rotation of a pair of blades to create an optical shutter. The present invention moves an optical element along the optical axis, which is coaxial with the stage force vector and the center of mass. The present invention is cylindrically symmetric.
Steiger 5,779,455 (July 1998) teaches about a “device for guiding and centering a machine component”. Steiger is differentiated from the present invention by both purpose and means. Steiger describes using a double set of planar flexures to guide a piston. An alternating current linear motor is used to turn the device into a reciprocating pump. Steiger does not use a position feedback element to allow for position control. Steiger does not use a moving coil motor to maximize performance. Most importantly, Steiger doesn't provide a centrally located clear aperture that would make it useful for mounting an optical element.
Donahoe et al 6,129,527 (October 2000) discloses an “electrically operated linear motor with integrated flexure spring and circuit for use in reciprocating compressor”. Donahoe is differentiated from the present invention by both purpose and means. Donahoe is also describing a reciprocating compressor. It does have a moving coil motor and planar flexures, but, the flexures are used as springs and there is no means to precisely control position. The device also doesn't have a central clear aperture or a means to control the position of the moving coil.
Schweizer 5,438,451 (August 1995) teaches about a “linearly fine-adjustment stage”. Schweizer is differentiated from the present invention by both purpose and means. Schweizer describes using a piezoelectric translator and elastic elements to guide the stage plate all through a central axis. Schweizer does not have a clear aperture on the axis, and flexures are not used to guide a voice coil with a position sensor.
Bohdan 4,704,712 (November 1987) teaches about a “low-friction slide apparatus for optical disc translation stage”. Bohdan is differentiated from the present invention by both purpose and means. Bohdan describes using a linear motor and a linear bearing but they are also off-axis from where an optic could be mounted.
Kaisha 6,055,116 (May 2000) teaches about a “multi-stage extension type zoom lens barrel”. The goal of Kaisha is to move an optical element linearly along the optical axis. The device does have a clear aperture on the axis. The device is guided concentrically about the optical axis. However, the constraint means is a large diameter screw thread. The drive means is an external rotary electric that drives a screw to create linear motion. The present invention used a position controlled voice coil motor guided by planar flexures.
Other References Cited4,461,984July 1984Whitaker5,040,372August 1991Higham5,980,211November 1999Tojo4,538,964September 1985Brown5,492,313February 1996Pan